Numerous pediatric disorders and surgical procedures performed on children lead to pain states yet it is well known that current pharmacological treatments for pain have adverse effects in children such as mild nausea or vomiting but also more severe side effects like respiratory depression and even death. Thus in order to develop more appropriate therapies for pain in children, a better understanding of how particular sensory afferent populations may contribute to pediatric pain states is of utmost importance. While much is known about the functional properties and plasticity of cutaneous nociceptors following peripheral injuries in adults, relatively little is known about the functiona properties of sensory afferents during development and the mechanisms of sensitization after peripheral injury. The main goal of this proposal is to functionally characterize cutaneous sensory afferents throughout development in naive mice and in models of postnatal inflammation, and begin to determine some of the mechanisms involved with the changes in sensory afferents. In order to determine this, we developed an ex vivo hairy skin, saphenous nerve, dorsal root ganglion (DRG), spinal cord recording preparation in neonatal/ postnatal mice that enables us to comprehensively phenotype sensory fibers before and after cutaneous injury. In Specific Aim 1, we will first analyze the functional, anatomical, and neurochemical phenotypes of these afferents at various times during postnatal development using combinations of ex vivo recording and immunocytochemical analyses. Changes in function will then be correlated with alterations in mRNA and protein expression of various receptors/ channels thought to be involved in sensory function in the DRGs. Next, in Specific Aim 2, we will perform similar studies as described in SA1 except we will analyze the comprehensive phenotypes of sensory afferents after hairy skin injection of carrageenan at different times during postnatal development and correlate these data with changes in gene expression in the DRGs to determine the potential mechanisms of the observed functional changes in cutaneous afferents. These experiments will enable us to characterize the changes in all types of cutaneous sensory neurons throughout development and during peripheral inflammation, and potentially identify unique age-dependent mechanisms associated with how developing sensory neurons respond to injury. These studies will establish the foundation of future experimentation using in vivo siRNA- mediated knockdown of genes in single peripheral nerves in conjunction with ex vivo recording preparations where we will be able to analyze the roles of changes in specific receptors/ channels during normal (uninjured) development and during different times of postnatal cutaneous inflammation. These and future studies will allow us to better understand how changes in sensory fibers impact pediatric pain and may also lead to the establishment of more suitable treatments for pain in children.